1. Field of the Invention
This invention pertains generally to devices and methods for holding and centering an object, and more particularly to a push-type expanding mandrel apparatus which holds and centers a machined part by exerting an outward force against an internal portion of the machined part. The invention allows quick, releasible attachment of the machined part to an expanding mandrel, and automatically centers the machined part during attachment to the expanding mandrel.
2. Description of the Background Art
Modern computer numerically controlled (CNC) machines are designed to precisely move a cutting tool along a predetermined path relative to a workpiece during machining of the workpiece. Advanced CNC machine tools have multiple spindles which allow two or more workpieces to be machined simultaneously. The holding devices for the workpieces must be able to quickly and precisely position and center workpieces in exactly the same spot or position each time a workpiece is exchanged.
Numerous devices have been developed to hold and center workpieces. These devices include collapsible-type mechanisms wherein a collet or chuck tightens onto a portion of a workpiece, and expansible-type mechanisms wherein an expandable collet or chuck member is inserted into an internal bore or opening of a workpiece and expanded therein to grip or hold the workpiece on the expandable member. However, previously known devices for holding and centering workpieces have proven deficient in various respects. Particularly, the procedures for attaching and detaching the workpiece from the devices are relatively time consuming and complex, and can require the tightening and loosening of multiple parts with special chuck tools in order to attach and detach the workpieces, which adds to the time and cost ultimately required for preparation of machined parts. Another problem is that many devices are complex in design and include numerous movable parts which are subject to wear and failure. A further deficiency in currently available holding devices is that accurate centering of the workpiece is generally not provided quickly or automatically. The aforementioned drawbacks hinder the effective use of currently available holding devices with the advanced CNC machine tools used in modern manufacturing operations.
Accordingly, there is a need for a push-type expanding mandrel apparatus which quickly and releasibly holds a workpiece, which quickly and automatically centers a workpiece, and which is suitable for use with high speed, high precision CNC machine tools. The present invention satisfies those needs, as well as others, and generally overcomes the deficiencies found in the background art.